Solder has widely been used as a conductive joint material used for mounting an electronic component.
Sn—Pb-based solder has conventionally generally been employed as solder. Recently, however, instead of the Sn—Pb-based solder, what is called Pb-free solder not containing Pb has widely been used.
PTD 1 discloses an electronic device including such solder not containing Pb and a method of manufacturing the same.
This PTD 1 describes a method of manufacturing an electronic device, including the step of forming a solder bump on a semiconductor chip with the use of a solder joint material containing (a) a first metal containing at least Bi, (b) an alloy of a second metal and a third metal, and (c) a third metal, the second metal being capable of making an intermetallic compound with Ni.
When a solder bump is formed with the solder joint material as in PTD 1, however, Ni and Bi react with each other because Ni or an Ni—P alloy is used in a barrier metal layer and hence a needle-shaped crystal is formed on a surface of the solder bump. Therefore, the surface of the solder bump does not have gloss and it is difficult to inspect a state of formation of a solder bump with such an optical method as a method with the use of an image sensor. In addition, when soldering is carried out with the use of a solder bump having a needle-shaped crystal formed on a surface, soldering high in reliability cannot be achieved.
PTD 2 discloses an electronic component (or a substrate) as an electronic component (or a substrate) to be joined to a substrate with the use of a Bi-based solder alloy not containing Pb but containing 80 mass % or more of Bi, in which a Zn metallized layer having a thickness from 0.05 to 8.00 μm or an Sn metallized layer having a thickness from 0.05 to 3.00 μm is formed on an Ni-containing layer which is an uppermost layer of the electronic component (or the substrate), and further discloses an electronic component (or a substrate) in which a second metallized layer having a thickness from 0.05 to 1.00 μm and selected from among Ag, Au, and Cu is formed on the Zn metallized layer or the Sn metallized layer.
In PTD 2, however, even though the Zn metallized layer or the Sn metallized layer is formed on the Ni-containing layer of the electronic component (or the substrate), for solder joint, solder joint should be carried out by separately externally supplying a Bi-based solder alloy containing 80 mass % or more of Bi, and application to a method of forming a solder bump on an electrode and carrying out solder joint with this solder bump itself (without externally supplying a solder joint material) cannot be made as in BGA mounting.
PTD 1: Japanese Patent Laying-Open No. 2010-129664
PTD 2: Japanese Patent Laying-Open No. 2011-238720